340 Mr. G. DdUmau on Arvicantliis abyssiuicus 



Face and head quite as dark as back ; ocular rino:s and tip o£ 

 nose orange. Dorsal stripe practically absent, a faint sagges- 

 tion of a median line visible under certain conditions of 

 illumination. Flanks paler and greyer than back, the p:ile 

 greyish buff-colour gradually merging into the light under 

 surface. Backs of hands and feet brownish, washed with 

 buff. Ventral surface of body light greyish white, faintly 

 tinted wnth buff, the coloration irregular, as in niloticus. 

 Hairs of belly with slate-grey bases and light tips. Tail 

 short and well covered with hairs; dark blackish brown 

 above, dirty buff-coloured below. 



Skull like that of testicuJaris centralis ; supraorbital ridges 

 more developed and with longer p.ilatal foramina. 



Dimensions of the type (measured in the flesh) : — 



Head and body 155 mm. ; tail 143 ; hind foot 33 ; ear 17. 



Skull : greatest length 35' 4 ; basilar length 29*2 ; con- 

 dylo-incisive length 33*9 ; zygomatic breadth 17*2 ; inter- 

 orbital constriction o ; squamosal breadth of brain-case 14 ; 

 length of nasals 132; palatilar length 15-8; length of 

 palatal foramina 8 ; alveolar leiigtli of upper molar series 7-2. 



Hob. Kaka, north of Fashoda, Soudan. 



Type. Adult male. B.M. no. 1. 8. 8. 50. Original num- 

 ber 35. Collected on April 23rd, 1901, and presented to 

 the British Museum by R. M. Hawker, Esq. 



This species is represented in the Museum collection by 

 three specimens — two from Kaka and one from Fashoda ; 

 they all present the same exceedingly dark-coloured pelage, 

 and are quite unlike any of the testicularis group. In general 

 characters this form appears to be intermediate between 

 niloticus and testicularis^ possessing tlie short tail and general 

 colouring of niloticus and with cranial characters more like 

 those of testicularis. It is at present impossible to decide 

 the exact relationship of this new species to the other forms 

 of Arvicanthis inhabiting the Nile Valley ; probably it is 

 more nearly allied to testicularis than to the Egyptian 

 species. In general colour luctuosus is not uulike some of 

 the northern races of ah'/ssinicus, such as rubescens ; but on 

 account of the great differences in the general dimensions 

 and cranial measurements it cannot be considered as belonging 

 to the ahyssinicus group. 



(5) Arvicanthis niloticus, Desm. 



]803. Lemmus niloticus, E. Geoff. Cat. Mus. Paris (nom. uud.). 



1822. Arvicola niloticus, Desmarest, Ency. Method., Mamm. Siippl. 



p. 281. 



1823. Ilypudceus variegatus, Licht. Verz. Doubl. Berlin, p. 2. 



